The Chemokine Fractalkine Inhibits Fas-Mediated Cell Death of Brain Microglia

Neurocrine Biosciences, Inc., San Diego, CA 92121, USA.
The Journal of Immunology (Impact Factor: 4.92). 08/2000; 165(1):397-403. DOI: 10.4049/jimmunol.165.1.397
Source: PubMed


Fractalkine is a CX3C-family chemokine, highly and constitutively expressed on the neuronal cell surface, for which a clear CNS physiological function has yet to be determined. Its cognate receptor, CX3CR-1, is constitutively expressed on microglia, the brain-resident macrophages; however, these cells do not express fractalkine. We now show that treatment of microglia with fractalkine maintains cell survival and inhibits Fas ligand-induced cell death in vitro. Biochemical characterization indicates that this occurs via mechanisms that may include 1) activation of the phosphatidylinositol-3 kinase/protein kinase B pathway, resulting in phosphorylation and blockade of the proapoptotic functions of BAD; 2) up-regulation of the antiapoptotic protein Bcl-xL; and 3) inhibition of the cleavage of BH3-interacting domain death agonist (BID). The observation that fractalkine serves as a survival factor for primary microglia in part by modulating the protein levels and the phosphorylation status of Bcl-2 family proteins reveals a novel physiological role for chemokines. These results, therefore, suggest that the interaction between fractalkine and CX3CR-1 may play an important role in promoting and preserving microglial cell survival in the CNS.

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    • "Both isoforms of CX3CL1 have been shown to ligate CX3CR1 [22], [23], [26], [27]. CX3CL1 directly induces various microglial functions including migration [14], proliferation [28], inhibition of Fas-ligand-induced cell death [29], glutamate-induced neurotoxicity [30], [31] and inhibition of proinflammatory cytokines production [5], [16]. Recently, it was shown that the soluble form of CX3CL1 directly enhances microglial clearance of degenerated neuronal debris [31]. "
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    ABSTRACT: We aimed to investigate fractalkine (CX3CL1) protein expression in wild type (wt) retina and its alterations during retinal degeneration in mouse model (rd10) of retinitis pigmentosa. Forms of retinal protein CX3CL1, total protein and mRNA levels of CX3CL1 were analyzed at postnatal days (P) 5, 10, 14, 22, 30, 45, and 60 by Western blotting and real-time PCR. Cellular sources of CX3CL1 were investigated by in situ hybridization histochemistry (ISH) and using transgenic (CX3CL1cherry) mice. The immunoblots revealed that in both, wt and rd10 retinas, a membrane integrated ∼100 kDa CX3CL1 form and a cleaved ∼85 kDa CX3CL1 form were present at P5. At P10, accumulation of another presumably intra-neuronal ∼95 kDa form and a decrease in the ∼85-kDa form were observed. From P14, a ∼95 kDa form became principal in wt retina, while in rd10 retinas a soluble ∼85 kDa form increased at P45 and P60. In comparison, retinas of rd10 mice had significantly lower levels of total CX3CL1 protein (from P10 onwards) and lower CX3CL1 mRNA levels (from P14), even before the onset of primary rod degeneration. ISH and mCherry reporter fluorescence showed neurons in the inner retina layers as principal sites of CX3CL1 synthesis both in wt and rd10 retinas. In conclusion, our results demonstrate that CX3CL1 has a distinctive course of expression and functional regulation in rd10 retina starting at P10. The biological activity of CX3CL1 is regulated by conversion of a membrane integrated to a soluble form during neurogenesis and in response to pathologic changes in the adult retinal milieu. Viable mature neurons in the inner retina likely exhibit a dynamic intracellular storage depot of CX3CL1.
    Full-text · Article · Sep 2014 · PLoS ONE
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    • "One hypothesis is that the interaction of the neuron-expressed FKN and its corresponding receptor, CX3CR1, which is found on microglia, leads to an inhibition of microglial destructive inflammation [4,5,20,21]. Treatment of microglia with FKN in vitro, for example, provokes an inhibition of cell death mechanisms through Fas ligand-induced cell death and other pro-apoptotic mechanisms [22]. Furthermore, it has been shown in a cell culture model that survival of hippocampal neurons can be induced by the presence of FKN via the protein kinase Akt pathway [23]. "
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    ABSTRACT: The chemokine fractalkine (CX3CL1, FKN) is involved in neural-microglial interactions and is regarded as neuroprotective according to several in vivo studies of inflammatory and degenerative states of the brain. Recently, an association with outcome in human ischemic stroke has been proposed. In this study, we aimed to investigate the temporal pattern of FKN levels in acute ischemic stroke in relation to stroke severity and outcome. FKN levels were measured in plasma specimens of fifty-five patients with acute ischemic stroke. Blood was available for time points 6 hours (h), 12 h, 3 days (d), 7 d and 90 d after stroke onset. Clinical outcome was evaluated using the modified Rankin Scale (mRS) at 7 d and 90 d. The time course of FKN significantly differs depending on stroke severity, with higher FKN levels linked to a lower severity. FKN levels in patients with moderate to severe strokes differ significantly from controls. In outcome analysis, we found an association of dynamics of FKN with clinical outcome. Decrease of FKN is pronounced in patients with worse outcome. Multivariate analysis including stroke severity and stroke etiology revealed that deltaFKN between 6 h and 3 d is independently associated with mRS at 90 d. In addition deltaFKN is inversely correlated with the extent of brain damage, as measured by S100B. FKN dynamics are independently associated with stroke outcome. Further studies might give insight on whether FKN is actively involved in the inflammatory cascade after acute ischemic stroke.
    Full-text · Article · Apr 2014 · Journal of Neuroinflammation
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    • "This is also accompanied by elicitation of chemokines such as MCP-1 by resident CNS cells including neurons, astrocytes and microglia. Chemokines also have the potential to recruit peripheral leukocytes across the BBB into the brain parenchyma [28]. This property of monocytes can be exploited to deliver exogenous genes of interest into the brain for neurotherapy [29]. "
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    ABSTRACT: HIV-1 associated dementia remains a significant public health burden. Clinical and experimental research has shown that reduced levels of brain-derived neurotrophic factor (BDNF) may be a risk factor for neurological complications associated with HIV-1 infection. We are actively testing genetically modified macrophages for their possible use as the cell-based gene delivery vehicle for the central nervous system (CNS). It can be an advantage to use the natural homing/migratory properties of monocyte-derived macrophages to deliver potentially neuroprotective BDNF into the CNS, as a non-invasive manner. Lentiviral-mediated gene transfer of human (h)BDNF plasmid was constructed and characterized. Defective lentiviral stocks were generated by transient transfection of 293T cells with lentiviral transfer plasmid together with packaging and envelope plasmids. High titer lentiviral vector stocks were harvested and used to transduce human neuronal cell lines, primary cultures of human peripheral mononocyte-derived macrophages (hMDM) and murine myeloid monocyte-derived macrophages (mMDM). These transduced cells were tested for hBDNF expression, stability, and neuroprotective activity. The GenomeLab GeXP Genetic Analysis System was used to evaluate transduced cells for any adverse effects by assessing gene profiles of 24 reference genes. High titer vectors were prepared for efficient transduction of neuronal cell lines, hMDM, and mMDM. Stable secretion of high levels of hBDNF was detected in supernatants of transduced cells using western blot and ELISA. The conditioned media containing hBDNF were shown to be protective to neuronal and monocytic cell lines from TNF-α and HIV-1 Tat mediated cytotoxicity. Lentiviral vector-mediated gene transduction of hMDM and mMDM resulted in high-level, stable expression of the neuroprotective factorBDNF in vitro. These findings form the basis for future research on the potential use of BDNF as a novel therapy for neuroAIDS.
    Full-text · Article · Feb 2014 · PLoS ONE
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